1. Field of the Invention
The present invention relates in general to crack detection techniques, and in particular to a new and useful ultrasonic technique for determining crack orientation and detecting cracks using horizontally polarized shear waves.
2. Description of the Related Art
To the knowledge of the applicant no other ultrasonic technique exists that can quantitatively determine the orientation of a crack, that is, the direction of a crack axis of a crack at a given point without moving the ultrasonic transducer from a fixed location.
Commonly used ultrasonic techniques involve the detection of a signal through reflection off of the crack surface. These signals can be weak in amplitude and may be easily missed due to many factors related to both the crack orientation relative to the ultrasonic beam and the bulk material acoustic properties. A common problem found in these techniques is that if no signal is present, the operator may assume the material to be free of cracks, when in fact cracks may indeed exist.
One prior art reference relating to the testing of materials through ultrasound is J. Krautkramer & H. Krautkramer, Ultrasonic Testing of Materials, Springer-Verlag (1969) pp. 7-11,463.
U.S. Pat. No. 5,125,272 described an ultrasonic tip diffraction technique for determining the depth of a surface-opening crack. Longitudinal ultrasonic waves are transmitted parallel to and along the crack with measurement of travel time of tip diffracted waves being used to determine the depth of the crack.